vfslookup.c

/*
 * Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
 *      The President and Fellows of Harvard College.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * VFS operations relating to pathname translation
 */

#include <types.h>
#include <kern/errno.h>
#include <limits.h>
#include <lib.h>
#include <synch.h>
#include <vfs.h>
#include <fs.h>
#include <vnode.h>

static struct vnode *bootfs_vnode = NULL;

/*
 * Helper function for actually changing bootfs_vnode.
 */
static
void
change_bootfs(struct vnode *newvn)
{
        struct vnode *oldvn;

        oldvn = bootfs_vnode;
        bootfs_vnode = newvn;

        if (oldvn != NULL) {
                VOP_DECREF(oldvn);
        }
}

/*
 * Set bootfs_vnode.
 *
 * Bootfs_vnode is the vnode used for beginning path translation of
 * pathnames starting with /.
 *
 * It is also incidentally the system's first current directory.
 */
int
vfs_setbootfs(const char *fsname)
{
        char tmp[NAME_MAX+1];
        char *s;
        int result;
        struct vnode *newguy;

        vfs_biglock_acquire();

        snprintf(tmp, sizeof(tmp)-1, "%s", fsname);
        s = strchr(tmp, ':');
        if (s) {
                /* If there's a colon, it must be at the end */
                if (strlen(s)>0) {
                        vfs_biglock_release();
                        return EINVAL;
                }
        }
        else {
                strcat(tmp, ":");
        }

        result = vfs_chdir(tmp);
        if (result) {
                vfs_biglock_release();
                return result;
        }

        result = vfs_getcurdir(&newguy);
        if (result) {
                vfs_biglock_release();
                return result;
        }

        change_bootfs(newguy);

        vfs_biglock_release();
        return 0;
}

/*
 * Clear the bootfs vnode (preparatory to system shutdown).
 */
void
vfs_clearbootfs(void)
{
        vfs_biglock_acquire();
        change_bootfs(NULL);
        vfs_biglock_release();
}


/*
 * Common code to pull the device name, if any, off the front of a
 * path and choose the vnode to begin the name lookup relative to.
 */

static
int
getdevice(char *path, char **subpath, struct vnode **startvn)
{
        int slash=-1, colon=-1, i;
        struct vnode *vn;
        int result;

        KASSERT(vfs_biglock_do_i_hold());

        /*
         * Locate the first colon or slash.
         */

        for (i=0; path[i]; i++) {
                if (path[i]==':') {
                        colon = i;
                        break;
                }
                if (path[i]=='/') {
                        slash = i;
                        break;
                }
        }

        if (colon < 0 && slash != 0) {
                /*
                 * No colon before a slash, so no device name
                 * specified, and the slash isn't leading or is also
                 * absent, so this is a relative path or just a bare
                 * filename. Start from the current directory, and
                 * use the whole thing as the subpath.
                 */
                *subpath = path;
                return vfs_getcurdir(startvn);
        }

        if (colon>0) {
                /* device:path - get root of device's filesystem */
                path[colon]=0;
                while (path[colon+1]=='/') {
                        /* device:/path - skip slash, treat as device:path */
                        colon++;
                }
                *subpath = &path[colon+1];
                
                result = vfs_getroot(path, startvn);
                if (result) {
                        return result;
                }

                return 0;
        }

        /*
         * We have either /path or :path.
         *
         * /path is a path relative to the root of the "boot filesystem".
         * :path is a path relative to the root of the current filesystem.
         */
        KASSERT(colon==0 || slash==0);

        if (path[0]=='/') {
                if (bootfs_vnode==NULL) {
                        return ENOENT;
                }
                VOP_INCREF(bootfs_vnode);
                *startvn = bootfs_vnode;
        }
        else {
                KASSERT(path[0]==':');

                result = vfs_getcurdir(&vn);
                if (result) {
                        return result;
                }

                /*
                 * The current directory may not be a device, so it
                 * must have a fs.
                 */
                KASSERT(vn->vn_fs!=NULL);

                *startvn = FSOP_GETROOT(vn->vn_fs);

                VOP_DECREF(vn);
        }

        while (path[1]=='/') {
                /* ///... or :/... */
                path++;
        }

        *subpath = path+1;

        return 0;
}

/*
 * Name-to-vnode translation.
 * (In BSD, both of these are subsumed by namei().)
 */

int
vfs_lookparent(char *path, struct vnode **retval,
               char *buf, size_t buflen)
{
        struct vnode *startvn;
        int result;

        vfs_biglock_acquire();

        result = getdevice(path, &path, &startvn);
        if (result) {
                vfs_biglock_release();
                return result;
        }

        if (strlen(path)==0) {
                /*
                 * It does not make sense to use just a device name in
                 * a context where "lookparent" is the desired
                 * operation.
                 */
                result = EINVAL;
        }
        else {
                result = VOP_LOOKPARENT(startvn, path, retval, buf, buflen);
        }

        VOP_DECREF(startvn);

        vfs_biglock_release();
        return result;
}

int
vfs_lookup(char *path, struct vnode **retval)
{
        struct vnode *startvn;
        int result;

        vfs_biglock_acquire();

        result = getdevice(path, &path, &startvn);
        if (result) {
                vfs_biglock_release();
                return result;
        }

        if (strlen(path)==0) {
                *retval = startvn;
                vfs_biglock_release();
                return 0;
        }

        result = VOP_LOOKUP(startvn, path, retval);

        VOP_DECREF(startvn);
        vfs_biglock_release();
        return result;
}